1. Field of the Invention
The present invention relates to an error detection method which is applied to e.g. digital communication.
2. Description of the Related Art
FIG. 3 is a flowchart for explaining the prior art error detection. As seen from FIG. 3, on a transmission side, speech is inputted (Step 14) and the speech is encoded (Step 15). The information (a bits) thus obtained is supplemented with an error detection code CRC (cyclic redundancy check code) (b bits) (Step 16). The information of (a+b) bits is encoded with an error correction code (Step 17) to be transmitted as one frame data (Step 18).
On a receiving side, the above error correction code is decoded (Step 20) and subjected to a CRC checking (Step 21) to detect an error (Step 22). Data having no error detected in the checking is subjected to a speech decoding processing on the decoded data (Step 23). The data with some error bits detected is subjected to sound processing, such as interpolation, using a previous frame or muting in place of the above speech decoding (Step 24). Both outputs are synthesized to be outputted as speech (Step 25).
However, in the above prior art error detection method, the CRC cannot detect the error in the case where one or more error bits are included in (a+b) bits. Thus, the prior art error detection method cannot provide error detection with high accuracy.
For example, when assuming a generator polynomial G (x) represented by EQU G(x)=1+x+x.sup.2 +x.sup.4 +x.sup.5 +x.sup.7
and assuming an error pattern represented by a polynomial EQU e(x)=1+x.sup.2 +x.sup.8 +x.sup.9
Then the above e(x) can be transformed into EQU e(x)=(1+x+x.sup.2 +x.sup.4 +x.sup.5 +x.sup.7)(1+x+x.sup.2).
In this case, e(x) can be divided by G(x) so that the CRC checking will detect e(x) as a correct pattern. Therefore, although the error as many as 4 (four) bits is included in (a+b) bits, the error detection cannot be made.
The present invention intends to solve the above conventional problem, and an object of the present invention is to provide an excellent error detection method which can surely detect the error for the data including the error pattern as mentioned above.